Most newly manufactured cotton fabrics and cotton blend fabrics have a handle that is rather hard and stiff unless they are treated with finishing components. Furthermore, the fabric surface is not always smooth due to small fuzzy fibers protruding from the individual cotton fibers. In addition, after a relatively short period of wear, collections of lint appear on the surface (surface linting) giving the appearance of "pills" on the surface which causes the fabric to have an unappealing, worn look. In polyester fabrics, this phenomena is actually "pilling" and provides a similar unappealing fabric appearance. The term "pilling" will also apply to cellulosic fabrics in the instant application.
Fabric softness and smoothness can be obtained by using finer, i.e., higher count value, yarns in the manufacture of a given fabric. A second method, building on the first approach is to use yarns prepared by the ring spinning process as opposed to the less expensive open-end process. However, the resulting cost is higher and fabric output decreases concurrently with the yarn count.
A less expensive way of ensuring a soft and smooth fabric "handle" is to impregnate the finished fabric with a softening agent, typically a cationic, sometimes silicone-based, surface active compound. However, this treatment does not remove pills and fuzz. Furthermore, the fabric obtains a somewhat greasy "handle"and is not wash-proof, and its moisture absorbency is often considerably reduced. This approach can have a negative influence on other wet processing steps, notably in causing an uneven dye uptake by the finished fabric.
Another known method for obtaining a soft and smooth fabric is treating cellulosic fabrics with cellulases. See Bazin et al., "Enzymatic Bio-Polishing of Cellulosic Fabric," presented at the 58th Congress of the Association of Chemists and the Textile Industry in Mulhouse, France (Oct. 25, 1991) and Asferg et al., "Softening and polishing of cotton fabrics by cellulase treatment," ITB Dyeing/Printing/Finishing (February 1990).
Cellulase treatment of the fabric surface improves fabric quality with respect to handle and appearance without loss of fabric wettability. The most important effects are less fuzz and pilling, increased gloss/luster, improved fabric handle, increased durable softness and improved water absorbency. These effects are referred to as biopolishing effects.
Various methods involving cellulase treatment have been disclosed in the art. For example, WO 9320278 discloses that biopolishing is achieved during the manufacture of cellulosic fabrics by successive (1) cellulase treatment of the fabric without significant mechanical treatment, then (2) mechanical treatment. The benefit of mechanical action is also disclosed in Cavaco-Paulo et al., 1994, Biocatalysis 10:353-360. Cavaco-Paulo et al., 1996, Textile Res. J. 66:287-294 discloses that at low agitation levels, pretreatment with monocomponent endoglucanase did not cause significant weight loss in a cotton fabric. At high agitation levels, significant weight loss was observed along with microfibrillar material torn away from the fiber surface.
Although this improved removal of surface fibers and fuzz is satisfactory in the laboratory, the textiles industry is moving toward the input of less mechanical action in the batch equipment now in operation. By not using mechanical action, there is less disturbance of the fabric surface presenting less opportunity for pilling and an unsatisfactory aesthetic appearance of the fabric when purchased by the customer. The outgrowth of this change is that the more aggressive multicomponent cellulases like those produced by T longibrachiatum are used to minimize pilling in the treated fabric For example, WO 9412578 discloses the treatment of a cellulosic fabric comprising (a) a first treatment with a cellulase to achieve a weight loss of 0.05-10 wt % of the fabric; (b) a second treatment with a cellulase to achieve a weight loss of 0.05-10 wt % of the fabric after step (a).
Cellulase treatment has also been found to reduce lint. U.S. Pat. No. 5,466,601 discloses a process that selectively removes embedded cellulose lint precursors from a cotton fabric by applying a cellulase solution continuously during the manufacturing process.
In the batch processing of cotton fabrics, namely interlock knits, the cellulase treatment has been applied at the end of the processing process, on the scoured, bleached, and dried fabrics (See Cavaco-Paolo et al, above). In some cases, the cellulase treatment has been attempted after the dyeing step with mixed results (W. R. Goynes et al, Textile Chemist and Colorist, December 1996, p. 25-29) on either the finished fabric, or after conversion to garment form. Not much attention given to the morphology or the chemical content of the cuticle and primary wall of the cotton fiber. Published reports describing the make-up of these parts of the cotton fiber describe the presence of various lipids, protein, and carbohydrate polymers including polygalacturonic acid partially esterified as the methyl ester. (Carpita and Gibeaut, The Plant Journal (1993) 3(1), 1-30).
During the course of scouring and alkaline peroxide bleaching/brightening certain chemical changes will occur in both the cuticle and primary fiber wall. These changes are important to the final acceptance of fabric, and how it behaves in further processing and final use. During the application of caustic, in either the scouring or bleaching/brightening process, the fiber wall would undergo a swelling process due to the charged carbohydrate polymers present, or due to the oxidation caused by the action of peroxide.
Once dried, however, the matrix formed by these polymers could hinder rehydration and access to the fibrils/microfibrils upon which the cellulase action is necessary to remove the materials which later cause the pilling effect. This same effect is known in wood fibers and is termed "hornification", which implies that the drying of the pulp fiber wall so changes the subsequent rehydration as to significantly impede water regain. This is of some consequence in the processing of recycled fibers and their reconversion into paper. This same effect, when applied to cotton fibers after they have been once rehydrated and dried, is a way to explain the need for higher levels of mechanical agitation to achieve a measurable effect with some classes of cellulases.
It is an object of the present invention to provide an improved enzymatic process for treating cellulosic fabrics.
It is also an object of the invention to reduce pilling of a fabric during subsequent launderings.
It is also an object of the present invention to improve the uniformity and rate of dye uptake during the dyeing stage of a dyed fabric.